Environmental Burden of Disease from Exposure to Lead in Ireland

The WHO Environmental Burden of Disease (EBD) methodology was used to assess burden of disease from lead exposure in Ireland. The aim was to produce a national baseline assessment and to evaluate whether intervention was required.

The outcomes used for children were IQ loss and resulting rates of mild mental retardation (MMR), rates of anaemia, and gastrointestinal symptoms were calculated for children. For adults, raised blood pressure as an indicator for risk of cardiovascular disease was used. Mean blood lead levels from a survey of a rural population living beside an old mining site were used and assumed to be representative of urban exposures (Adults = 3.0μg/dL, n=341; pre-school children= 2.7μg/dL, n=84). Communities beside mining sites have been found to have similar levels of exposure to urban populations. Urban populations are assumed to have a greater proportion of their exposure from transport sources so estimates were constructed with and without the use of a correction factor to account for annual reductions since the ban on lead in gasoline in 2000. Assuming a normal distribution of the log-transformed means, the proportion of the population at each blood Pb interval was estimated, and rates of disease for each health outcome were mapped to each interval, based on the WHO dose-response estimates.

The attributable incidence rates of MMR in children was low (0.25/1000), as were rates of gastrointestinal symptoms (0.06/1000) and anaemia (0.04/1000). The Attributable Fractions for cerebrovascular and hypertensive disease in men was 1% and 0% for ischaemic heart disease and other heart disease in men. The Attributable Fraction for all cardiovascular outcomes in women was 0%.

Discussion & Conclusions:
The study population used is not representative of the Irish population. Populations adjacent to mining sites do not experience exposures comparable to those observed in communities beside other point sources, such as smelters. The survey population may be more representative of rural exposures, making the current assessment an underestimate. Analysis and comparison with similar urban and rural populations will be conducted to determine whether the current assessment should be assumed as a low, medium or high estimate. In countries with long-standing legislative controls on the use of lead, exposure of the general population will be low. Locally high levels due to point sources and exposure of children living in degraded housing are likely to be more important. Targeted surveillance of identified 'at risk' groups as recommended by the CDC in the US may be more practical for informing public health than the wider EBD assessment. The study highlighted the difficulty in conducting epidemiology in the absence of any biomonitoring in Ireland.